I think people experiment a temporal change of behavior motivated for the love to someone, but if the bad behavior is not motivated by a real desire to become in a better version of themselves then that change is not gonna last.
The love has different stages; is easier to change on the first three years when the love is passionate and wild, because you want to please the other person and at the same time you receive affection, sex, and positive attention for doing it. But the next stage requires commitment and if the person is not deeply interested in the other, or hasn't supported his change of behavior by his own wish or motivation then there's always gonna be the temptation to go back to how he/she used to be.
There are some exceptions, but I think is not the rule.

If you love someone and you can't change for them, remember the change here is supposed to be a positive change and not a selfish change for the interest of the demanding partner, then it's not truly a pure love affair. But when it's a real love, I do believe that we can do anything to help make our love affair to be more strong.

But let's take into consideration when one of the parties is just being too selfish and wants to change their partner to a dummy all in the name of relationship and love, that's practically wrong and personally I won't be able to do such because it's more like losing my personality and becoming a different person.

I don't think someone can change, maybe for a while but in the end, their character and real behavior will rise on top. People do not change they adapt to a situation but when they feel frightened or just hate the actual situation they change back.

Indeed. I believe that people can change if they love someone because I experienced it to the girl I loved once before. She loves to read a books, eating in some fancy restaurant, she also has a good grade in school and I am exactly opposite to what she is Im just a boy who loves to play computer games and not really good at socializing. But when I started to like her I suddenly realize that I started to do what she do and love what she loved. And then the times go on she fell inlove to me and started a relationship happy  memories built in but after 2 years everything has changed she didnt love me anymore. And I started to change again but for worst I always go to casino, bar just to cheer my self up. Loving someone can change you but It can also change you by not loving you back.